This invention relates to an expandable router.
A broadcast switch for distributing a signal from one source to multiple destinations typically has N signal input terminals connected to respective signal sources, M signal output terminals connected to respective destinations and a switch core which can direct an input signal received at any one of the N input terminals to a group {m1} of output terminals. The switch will normally include interface circuitry for adapting the input signal to the operating requirements of the switch core and for restoring the output signal of the switch core to the same form as the input signal. Preferably, the switch core is non-blocking, i.e. the connection between any one of the N input terminals and any one of the M output terminals can be made regardless of the existing connection(s) made by the switch core. Ideally, the switch core can also direct the signal received at a second of the N input terminals to a group {m2} of output terminals, where {m1} and {m2} are mutually exclusive. A rectangular crosspoint matrix composed of N input buses, M output buses and Nxc3x97M switch elements, where each switch element can connect a unique combination of one input bus and one output bus, can be used to provide a switch core that meets these requirements. A rectangular crosspoint matrix works well as a switch core but is subject to the disadvantage that the cost of the switch core depends roughly on the number of switch elements, and hence on the product of the number of inputs and the number of outputs, rather than on the sum of the number of inputs and the number of outputs.
It is also known to use time division multiplexing (TDM) in a switch core for directing an input signal to a group of outputs. Referring to FIG. 1, serial digital input signals from four sources are supplied to serial in, parallel out (SIPO) registers 10 which generate parallel output data words. Each SIPO is assigned a position in a sequence that contain all the SIPOs. Typically, the assigned position of a SIPO reflects the spatial location on the back panel of the routing switch of an input terminal, such as a connector, to which the SIPO is connected. A controller (not shown) read enables the SIPOs sequentially and accordingly the parallel output data words are placed sequentially on a bus 12. The controller controls the read enable supplied to the SIPOs and the state of the bus 12 so that the data words are placed on the bus in successive bus operating cycles. Consequently, the position of a data word from a particular SIPO in the sequence of bus operating cycles depends strictly on the assigned position of the SIPO The sequence of data words is written to successive addresses in a memory 14, and the address to which a data word is written depends strictly on the position of the data word in the sequence of bus operating cycles and hence on the spatial location of the input terminal at which the signal from which the data words were derived was received. The data words are read from the memory 14 in strict order of address and placed on an output bus 16 in respective time slots of the bus operating cycle as four interleaved parallel digital signals. Thus, the SIPO registers 10 and the memory 14 map the input terminals of the switch to different respective time slots in the operating cycle of the output bus 16. The output bus 16 is accessed by parallel in, serial out (PISO) registers 18 whose outputs are connected to the output terminals of the switch. Each register 18 accesses the bus 16 during one selected time slot of the bus operating cycle and thus selects the signal provided by one selected input terminal. Each PISO register 18 converts the parallel data of the selected signal to serial form and provides the serial data to the output terminal of the switch core.
The TDM switch core shown in FIG. 1 has some advantages over the rectangular crosspoint matrix, particularly with respect to cost of expansion. In the case of the TDM switch core, the cost of the switch core depends on the sum of the number of inputs and the number of outputs but the number of inputs that can be supported is limited by the bandwidth of the bus 16.
Referring to FIG. 2, the public telephone network is built around numerous switching offices each of which includes a point-to-point (i.e. non-broadcast) router 20 having bidirectional subscriber lines connected to the subscriber stations served by that switching office. The router 20 allows any one of the subscriber lines to be connected to any other subscriber line connected to that router. The router also has a so-called T1 line which is connected to a multiplexer-demultiplexer (mux-demux) 22 which also receives T1 lines from other routers and connects the several T1 lines to a common T3 line. The T3 line is connected over the backbone 24 of the public network to another T3 line which is connected to a mux-demux 26 at another switching office, which is spatially remote from the first switching office, the mux-demux 26 being connected by multiple T1 lines to multiple routers 28. The arrangement shown in FIG. 2 allows each subscriber station to be connected to each other subscriber station without need for a single enormous router to which every subscriber line is connected, but is subject to disadvantage because the routers are blocking, and consequently even though the subscriber line of a particular subscriber station might not be in use, it is not always possible to make a connection to that station.
According to a first aspect of the present invention there is provided a routing switch comprising a first router module having N1 signal input terminals, M1 signal output terminals, an expansion input terminal and an expansion output terminal and including a means for routing a signal received at any one of the N1 signal input terminals selectively to any one or more of the output terminals and for routing a signal received at the expansion input terminal selectively to any one or more of the N1 signal output terminals, and a second router module having N2 signal input terminals, M2 signal output terminals, an expansion input terminal and an expansion output terminal and including a means for routing a signal received at any one of the N2 signal input terminals selectively to any one or more of the output terminals and for routing a signal received at the expansion input terminal selectively to any one or more of the M2 signal output terminals, and wherein the expansion output terminal of the first router module is connected to the expansion input terminal of the second router module and the expansion output terminal of the second router module is connected to the expansion input terminal of the first router module.
According to a second aspect of the present invention there is provided a router module having N signal input terminals, M signal output terminals, an expansion input terminal and an expansion output terminal and including a router means for routing a signal received at any one of the N signal input terminals to any one or more of the output terminals and for routing a signal received at the expansion input terminal to any one or more of the M signal output terminals, the router means including a switch core for switching serial digital data streams, the switch core including N SIPO registers which convert serial digital data to parallel form, an input bus which reads the N SIPO registers sequentially, a first memory which buffers parallel data on the input bus to a first intermediate bus, a second memory which buffers parallel data on the first intermediate bus to a second intermediate bus, an output expansion interface connected to the first intermediate bus for supplying the parallel data on the first intermediate bus to the expansion output terminal, an input expansion interface for receiving data from the input expansion terminal and placing the data on the second intermediate bus, a third memory for buffering the data on the second intermediate bus onto an output bus, and M PISO registers for reading the output bus during selected time slots and converting the parallel data to serial form.
According to a third aspect of the present invention there is provided a router module having N signal input terminals, M signal output terminals, an expansion input terminal and an expansion output terminal and including a router means for routing a signal received at any one of the N signal input terminals to any one or more of the output terminals and for routing a signal received at the expansion input terminal to any one or more of the M signal output terminals, wherein the router module includes a switch core for switching serial digital data streams, the switch core including N1 SIPO registers which convert serial digital data to parallel form, an input expansion interface for receiving data from the input expansion terminal and providing parallel output data, a memory means which receives and temporarily stores parallel data provided by the N1 SIPO registers and parallel output data provided by the input expansion interface, an output expansion interface connected to the expansion output terminal, M PISO registers connected to the M signal output terminals, and memory output means for selectively providing data read from the memory means to the output expansion interface and the PISO registers.
According to a fourth aspect of the present invention there is provided a routing switch comprising n routers (n greater than 1) and wherein each router comprises p router modules (pxe2x89xa71) each having a plurality of signal input terminals, a plurality of signal output terminals, nxe2x88x921 expansion input terminals and nxe2x88x921 expansion output terminals and including a means for routing a signal received at any one of its signal input terminals to any one or more of its output terminals and for routing a signal received at any one of the expansion input terminals to any one or more of the signal output terminals, and an expansion interconnect network whereby each expansion output terminal of the ith router module (i=1 . . . p) of the jth router (j=1 . . . n) is connected to an expansion input terminal of ith router module of a router other than the jth router.